Rotationally Balanced Camshaft Assembly

ABSTRACT

A method for intentionally imbalancing one or more mass elements of a camshaft assembly to provide overall rotational balance to the assembly, also referred to herein as “zero balance”. Such intentional imbalance may be imparted to any element of a camshaft assembly. In a currently-preferred embodiment, one or more components of an improved camshaft phaser assembly are manufactured as rotationally unbalanced, either by intentionally forming an unbalanced component such as a sprocket wheel having added material or by removing non-functional material from an otherwise standard component. Because the camshaft phaser assembly has a unique and fixed angular relationship to the camshaft, zero balance can be readily and repeatedly achieved for all camshaft assemblies by correct manufacture of parts without requiring separate balancing for each individual camshaft assembly as manufactured.

RELATIONSHIP TO OTHER APPLICATIONS AND PATENTS

This application claims the benefit of U.S. Provisional Application No.61/203,895, filed Dec. 30, 2008.

TECHNICAL FIELD

The present invention relates to rotational balancing of an internalcombustion engine; more particularly, to rotational balancing of acamshaft assembly; and most particularly, to a rotationally balancedcamshaft assembly manufactured by using an intentionally unbalancedelement of the camshaft assembly, and especially a component of acamshaft phaser, to achieve rotational balance of the overall assembly.

BACKGROUND OF THE INVENTION

It is well known in the engine arts to achieve overall rotationalbalance of the crankshaft assembly of an internal combustion engine bystrategic removal of material from one or more rotational elements ofthe crankshaft assembly, such as a flywheel, a balancer, and/or thecrank throws. Heretofore, comparable rotational balancing of an enginecamshaft has not been disclosed. In the prior art, the diameter androtational mass of a camshaft assembly has not been sufficiently greatto cause unacceptable wear and vibration in an engine to warrantbalancing.

However, in some modern applications, it has been found that engine idlequality can be seriously impaired by camshaft rotational imbalance,especially for relatively small engines having two camshafts. In currentcam phaser applications, the design metric for cam phaser assemblyimbalance is typically lower than an OEM specified threshold value. Thisvalue varies by OEM. Other than the cam phaser itself, various othercomponents directly fixed to camshafts, including cam lobes, fuel pumplobes, and target wheels, can create additional overall rotationalimbalance in a complete camshaft assembly. Lastly, various drillings andmachined features, such as those for oil feeds, sensors, or tapped holeson the camshaft itself can create further rotational imbalance. Thecombined effects of these factors can result in camshaft assemblies thatare imbalanced above the threshold value.

Optimum system design would dictate that auxiliary components should beplaced along the camshaft in an orientation that favors better systembalance; however there are oftentimes overriding design considerationsthat do not favor camshaft balance. Imbalance of the camshaft assembly,as a rotating mass, can lead to excessive engine vibration. Thisvibration can lead to various end effects including premature cambearing wear, excessive wear on other mating valvetrain components, andexcessive engine noise. All of these effects are a concern over theentire engine RPM range, but the last effect is primarily a concern atidle condition when a vehicle is stationary and engine vibration andnoise can be easily perceived by occupants of the vehicle.

What is needed in the art is a method and apparatus for readilybalancing a camshaft assembly to reduce engine vibration and noise.

It is a principal object of the present invention to reduce enginevibration and noise, and to extend engine operating life.

SUMMARY OF THE INVENTION

Briefly described, a method in accordance with the present inventionintentionally imbalances one or more mass elements of a camshaftassembly to provide overall rotational balance to the assembly, alsoreferred to herein as “zero balance”. Such intentional imbalance may beimparted to any element of a camshaft assembly, including any newelement (counterweight) or plurality of elements provided expressly forthat purpose. In a currently-preferred embodiment, one or morecomponents of a camshaft phaser assembly are manufactured asrotationally unbalanced, either by intentionally forming an unbalancedcomponent such as a sprocket wheel having added material or by removingnon-functional material from an otherwise balanced component. Becausethe camshaft phaser assembly has a unique and fixed angular relationshipto the camshaft, zero balance can be readily and repeatedly achieved forall camshaft assemblies by correct manufacture of parts withoutrequiring separate balancing for each individual camshaft assembly asmanufactured.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described, by way of example, withreference to the accompanying drawings, in which:

FIG. 1 is an exploded isometric view of a prior art vane-type camshaftphaser;

FIG. 2 is an isometric view of a prior art camshaft assembly;

FIG. 3 is an isometric view of the prior art camshaft phaser shown inFIG. 1, partially in cutaway, showing the oil passages in the camshaftphaser, a basis for inherent rotational imbalance;

FIG. 4 is an isometric view of first embodiment of an unbalanced phasersprocket wheel in accordance with the present invention, showingaddition of material to cause the intentional imbalance;

FIG. 5 is an isometric view of a camshaft phaser including the sprocketwheel shown in FIG. 4;

FIG. 6 is an isometric view of a second embodiment of an unbalancedphaser sprocket wheel in accordance with the present invention, showingazimuthally progressive removal of material in the tooth root area; and

FIG. 7 is an isometric view of a third embodiment of an unbalancedphaser sprocket wheel in accordance with the present invention, showingremoval of material by machined features in the wheel hub area.

Corresponding reference characters indicate corresponding partsthroughout the several views. The exemplifications set out hereinillustrate currently preferred embodiments of the invention, and suchexemplifications are not to be construed as limiting the scope of theinvention in any manner.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The object of the present invention is to rotationally balance(zero-balance) a camshaft assembly using components within the camshaftassembly, preferably by intentional imbalancing of an incorporatedcamshaft phaser assembly. Re-balance can be accomplished using any ofthe non-functional areas of such components and/or by adding material ascounterweights. Both adding mass features and removing mass can affectimbalance and a combination of the two can be used to achieve the endresult. A secondary objective of the present invention is to accomplishthe abovementioned without an increase in part count, complexity, orcost. Because of its relatively large mass and diameter, the camshaftphaser assembly is a preferred site for creation of such componentimbalance.

Referring to FIG. 1, a typical prior art vane-type camshaft phaserassembly 10 includes a pulley or sprocket wheel (pulley/sprocket) 12 forengaging a timing chain or belt (not shown) operated by an enginecrankshaft (not shown). The upper surface 14 of pulley/sprocket 12 formsa first wall of a plurality of hydraulic chambers in the assembledphaser. A stator 16 is disposed against surface 14 and is sealed theretoby a first seal ring 18. Stator 16 is rotationally immobilized withrespect to pulley/sprocket 12. Stator 16 is provided with a plurality ofinwardly-extending lobes 20 circumferentially spaced apart for receivinga rotor 21 including outwardly extending vanes 22 which extend into thespaces between lobes 20. Hydraulic advance and retard chambers (notvisible in exploded drawing) are thus formed between lobes 20 and vanes22. A thrust washer 24 is concentrically disposed against rotor 21, andcover plate 26 seals against stator 16 via a second seal ring 28. Bolts30 extend through bores 32 in stator 16 and are received in threadedbores 34 in pulley/sprocket 12, immobilizing the stator with respect tothe pulley/sprocket. In installation to an engine camshaft, phaser 10 issecured via a central bolt (not shown) through thrust washer 24 which iscovered by cover plug 36 which is threaded into bore 38 in cover plate26.

A locking pin mechanism 40 comprises a hollow locking pin 42 having anannular shoulder 43, return spring 44, and bushing 46. Spring 44 isdisposed inside pin 42, and bushing, pin, and spring are received in alongitudinal bore 48 formed in an oversize vane 22′ of rotor 21, an endof pin 42 being extendable by spring 44 from the underside of the vane.A pin seat 47 is disposed in a well 49 formed in pulley/sprocket 12 forreceiving an end portion of pin 42 when extended from bore 48 torotationally lock rotor 21 to pulley/sprocket 12 and, hence, stator 16.The axial stroke of pin 42 is limited by interference of shoulder 43with bushing 46. A shallow channel 51 formed in pulley/sprocket 12extends from below seat 47 and intersects surface 14 in a region of thatsurface which forms a wall of a selected advance chamber in theassembled phaser. Thus, when oil is supplied to advance the rotor withrespect to the stator, oil also flows through channel 51 to bringpressure to bear on the end surface (axial face) 53 of pin 42, causingthe pin to be forced from seat 47 and thereby unlocking the rotor fromthe stator. Conversely, the pin defaults to the locked position wheneveroil pressure is below a threshold level.

Referring to FIG. 2, a prior art camshaft assembly 100 comprises atleast a camshaft 102 having a plurality of eccentric cam lobes 104, aplurality of shaft bearing surfaces 106, and a camshaft phaser assembly108 that may or may not be identical with camshaft phaser assembly 10.Camshaft phaser assembly 108 is mounted to the end of camshaft 102 in aunique and fixed azimuthal relationship. Assembly 100 may furtherinclude a target wheel 110 mounted on either the camshaft phaserassembly 108 (not shown) or on the opposite end of the camshaft as shownin FIG. 1.

Referring to FIG. 3, the oil passages 150 in a typical vane-typecamshaft phaser 108 are shown. Since oil is distributed to and withinthe cam phaser through oil galleries which are not symmetricallydistributed about the rotational axis 152 of the phaser, oil galleries,when filled with oil rather than the metal which is removed by theircreation, can create significant imbalance in a phaser.

Referring to FIGS. 4 and 5, in a first embodiment of an unbalancedcamshaft assembly element in accordance with the present invention, aphaser sprocket wheel 212 is formed having two asymmetrically-positionedradial ribs 260, causing wheel 212 to be unbalanced in direction 262with respect to axis 152. The mass and shape of ribs 260 ispredetermined as by modeling and/or experimentation to be justsufficient to offset a rotational imbalance in opposite direction 264 ina camshaft assembly in which a sprocket wheel 212 is an element, therebyproducing a net zero rotational imbalance in the camshaft assembly. FIG.5 shows an improved camshaft phaser assembly 208 incorporatingunbalanced sprocket wheel 212 for substitution for prior art camshaft isphaser 108 in prior art unbalanced camshaft assembly 100 (FIG. 2), inaccordance with the present invention, to yield an improvedrotationally-balanced camshaft assembly.

Presently-known embodiments utilize a powdered metal (sintered steel)sprocket with an added mass feature 260 to zero-balance a camshaftassembly. By utilizing powdered metal modified die features to form ribs260, overall zero balance in a camshaft assembly can be achieved withoutadded complexity, part count or cost.

Referring now to FIG. 6, in a second embodiment of an unbalancedcamshaft assembly element in accordance with the present invention, aphaser sprocket wheel 312 includes a progressive removal channel 370formed in the root area 372 of sprocket teeth 374, either by machiningor by casting, the net effect of removal channel 370 being to unbalancesprocket wheel 312 in direction 262 as in first embodiment 212 (FIGS. 4and 5).

Referring now to FIG. 7, in a third embodiment 412 of an unbalancedcamshaft assembly element in accordance with the present invention, aphaser sprocket wheel includes one or more machined features 470 in thehub 472 of sprocket wheel 412, the net effect of machined features 470being to unbalance sprocket wheel 412 in direction 262 as in firstembodiment 212 (FIGS. 4 and 5) by removal of material in a net oppositedirection.

Further, it will be appreciated by those of ordinary skill in the artthat rotational balancing of an otherwise unbalanced camshaft assemblymay be achieved by addition of one or more eccentrically-placedcounterweights (not shown) at any convenient point along the camshaft orwithin the camshaft phaser assembly.

The disclosed specific embodiments are only demonstrative of theinvention. Any component of a camshaft assembly, including but notlimited to a counterweight and the camshaft phaser assembly andfurthermore including but not limited to the sprocket wheel, stator,rotor, cover plate, and target or timing wheel, may be used forre-balancing, and many possible locations for mass addition/removal areavailable. Embodiment 212 (FIGS. 4 and 5) is zero-balanced with the camphaser in the default position such as is experienced at idle condition.Rotational mass balance or unbalance can also be achieved if so desiredwith the cam phaser in advance position, retard position or at anyintermediate position. In addition, the rotor assembly and the statorassembly of a camshaft phaser assembly can be mass-balanced orunbalanced independently, causing the phaser assembly to be massbalanced in all positions.

While the invention has been described by reference to various specificembodiments, it should be understood that numerous changes may be madewithin the spirit and scope of the inventive concepts described.Accordingly, it is intended that the invention not be limited to thedescribed embodiments, but will have full scope defined by the languageof the following claims.

While the embodiments as described are shown in a single camshaftarrangement, the invention is equally applicable in multiple camshaftarrangements and on intake or exhaust camshafts.

1. A method for forming a rotationally balanced camshaft assembly for aninternal combustion engine, the camshaft assembly including at least acamshaft having at least one eccentric cam, and a camshaft phaser, themethod comprising the steps of: a) determining the magnitude ofrotational imbalance of an unbalanced camshaft assembly; and b)adjusting the magnitude of rotational imbalance of at least onecomponent of said unbalanced camshaft assembly to compensate for saidmagnitude of rotational imbalance of said unbalanced camshaft assemblyto yield said rotationally balanced camshaft assembly.
 2. A method inaccordance with claim 1 wherein said at least one component is anelement of said camshaft phaser.
 3. A method in accordance with claim 2wherein said element is selected from the group consisting of sprocketwheel, stator, rotor, cover plate, and target wheel.
 4. A method inaccordance with claim 1 wherein said adjusting step includes the step offorming said at least one component in a predetermined unbalancedarrangement.
 5. A method in accordance with claim 4 wherein said formingstep includes addition of material to said at least one component tocause said predetermined unbalanced arrangement.
 6. A method inaccordance with claim 4 wherein said forming step includes subtractionof material from said at least one component to cause said predeterminedunbalanced arrangement.
 7. A method in accordance with claim 1 whereinsaid component is a counterweight added eccentrically to said camshaftassembly expressly to rotationally balance said camshaft assembly.
 8. Acamshaft assembly comprising a plurality of components wherein at leastone of said components is intentionally rotationally unbalanced suchthat said camshaft assembly is rotationally balanced.
 9. A camshaftassembly in accordance with claim 8 comprising at least a camshafthaving at least one eccentric cam, and a camshaft phaser, wherein saidat least one component is an element of said camshaft phaser.
 10. Acamshaft assembly in accordance with claim 9 wherein said element isselected from the group consisting of sprocket wheel, stator, coverplate, and target wheel.
 11. A camshaft assembly in accordance withclaim 9 wherein said at least one component is formed in a predeterminedunbalanced arrangement.
 12. A camshaft assembly in accordance with claim11 wherein said predetermined unbalanced arrangement includes additionof material to said at least one component.
 13. A camshaft assembly inaccordance with claim 11 wherein said predetermined unbalancedarrangement includes removal of material from said at least onecomponent.
 14. A camshaft assembly in accordance with claim 8 whereinsaid at least one component is a counterweight added eccentrically tosaid camshaft assembly expressly to rotationally balance said camshaftassembly.
 15. An internal combustion engine having at least one camshaftassembly wherein at least one component of said camshaft assembly isintentionally rotationally unbalanced in a predetermined unbalancedarrangement such that the overall camshaft assembly is rotationallybalanced.